1. Field of the Invention
The present invention generally relates to a process control apparatus that controls a control target.
Priority is claimed on Japanese Patent Application No. 2007-34609, filed Feb. 15, 2007, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In general, the process control apparatus controls a control target so that a measured value of the control target follows a predetermined value. The process control apparatus includes a control unit that controls the control target. In general, the control unit can be designed so that the measured value of the control target follows a predetermined value in the environment that the period of the disturbance is not specified. The conventional process control apparatus does control without consideration of periodic disturbance.
Automatica 2005, vol. 41, 4 pp. 563-574, I. D. Landau, A. Constantinescu, D. Rey, “Adaptive narrow band disturbance rejection applied to an active suspension—an internal model principle approach” discloses a method for designing the control unit using the internal model principle in order to reject the influence of the disturbance from the measured value.
FIG. 10 is a block diagram illustrating the configuration of a conventional process control apparatus. The conventional process control apparatus includes a control unit 100 that is designed using a PID control method. The control unit 100 controls a control target 200.
As show in FIG. 10, a setting value “r” and a measured value “y” of the control target 200 are input into a first summing point 101. The first summing point 101 generates at error signal “e” that represents the difference between the setting value “r” and the measured value “y”. The error signal “e” is input into the control unit 100. The control unit 100 generates the manipulated value “u” based on the error signal “e”. The manipulated value “u” does not include any operation amount that is to reject a periodical disturbance “p”. The manipulated value “u” and the periodical disturbance “p” are input into a second summing point 102. The manipulated value “u” and the periodical disturbance “p” are summed by the second summing point 102. The sum of the manipulated value “u” and the periodical disturbance “p” are input into the control target 200 so as to control the control target 200.
Japanese Patent No. 2982209 and Japanese Unexamined Patent Application, First Publications, Nos. 2004-303086 and 2005-273634 disclose conventional techniques using fuzzy control for rejecting periodical disturbances.
In accordance with the conventional process control apparatus, when the control unit, which is designed in the environment that the period of the disturbance is not specified, is incapable of rejecting the disturbance, thereby deteriorating the control performance of the control unit. The control unit, which is designed in the above-described method proposed by I. D. Landau, et al., is capable of rejecting the disturbance. A feedback loop L needs to be reconfigured to provide the control unit that is capable of rejecting the disturbance.
After the control unit that is capable of rejecting tile disturbance is provided and the feedback loop L is reconfigured, it is necessary for no need to reject disturbance to replace the control unit that is capable of rejecting the disturbance into other control unit that is designed in the circumstance that the period of the disturbance is not specified. The replacement of the control unit still needs to reconfigure the feedback loop L. In other words, switching on or off the disturbance rejection needs reconfiguration of the feedback loop L. It is necessary to stop operations of the control unit 100 and the control target 200 every time the feedback loop L is reconfigured for replacing the control unit.
The process control apparatus designed in accordance with the conventional method proposed by I. D. Landau, et al., is capable of rejecting the disturbance by an appropriate control when the periodical disturbance has a narrow frequency distribution. If the frequency distribution of the periodical disturbance is wide, the waterbed effect of frequency characteristic is caused. In this case, the control unit that is designed to reject the disturbance in a limited frequency band may emphasize the disturbance in the other frequency band.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved process control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.